An investigation into the source of the fatal fire at a Massachusetts assisted living facility last week classified the cause as "undetermined," though officials believe it was an accidental ignition

The person who lived in the room where the fire began is among the 10 people killed, according to the state fire marshal

The deadly blaze that broke out at an assisted living facility in Massachusetts earlier this month was sparked accidentally by either a malfunctioning oxygen machine or, possibly, a resident smoking,